U.S. patent number 5,429,251 [Application Number 08/124,248] was granted by the patent office on 1995-07-04 for semiconductor wafer end effector.
This patent grant is currently assigned to Legacy Systems, Inc.. Invention is credited to Robert R. Matthews.
United States Patent |
5,429,251 |
Matthews |
July 4, 1995 |
Semiconductor wafer end effector
Abstract
An end effector for holding or carrying semiconductor wafers
during wet processing is disclosed. The end effector holds a
plurality wafers with only two points of contact intruding onto the
front or back surface of the wafer, holding the wafer with
substantially no movement during processing at a slight angle from
vertical.
Inventors: |
Matthews; Robert R. (Richmond,
CA) |
Assignee: |
Legacy Systems, Inc.
(Richardson, TX)
|
Family
ID: |
22413707 |
Appl.
No.: |
08/124,248 |
Filed: |
September 22, 1993 |
Current U.S.
Class: |
211/41.18 |
Current CPC
Class: |
H01L
21/67313 (20130101) |
Current International
Class: |
H01L
21/673 (20060101); H01L 21/67 (20060101); A47F
007/00 () |
Field of
Search: |
;211/41 ;206/334,454
;118/500 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ramirez; Ramon O.
Assistant Examiner: Purol; Sarah L.
Attorney, Agent or Firm: Burns, Doane, Swecker &
Mathis
Claims
What is claimed is:
1. An end effector for supporting one or more semiconductor wafers
during wet processing with only two points of contact,
comprising:
two parallel, grooved engaging rails having corresponding linearly
aligned angled grooves adapted to engage and support a wafer at an
angle .theta. from perpendicular to said rails;
means for rigidly supporting said parallel rails in a parallel
configuration; and
a non-symmetrical gripper means for association with said grooves
holding said wafer at the angle .theta. from a perpendicular with
substantially no movement of the wafer in the grooves during wet
processing.
2. The end effector of claim 1, further comprising one or more
non-engaging rails parallel to said parallel grooved engaging
rails.
3. The end effector of claim 1, wherein said rigid supporting means
includes two end plates attached to said parallel engaging
rails.
4. The end effector of claim 1, wherein said end effector is made
of a woven carbon fiber composite.
5. The end effector of claim 1, further comprising a coating which
is applied by chemical vapor deposition or sputtering, wherein said
coating is polysilicon, silicon nitride, silicon carbide, carbon or
carbon nitride.
6. The end effector of claim 1, wherein said non-symmetrical
gripping means includes a plurality of tapered surfaces cut at
different angles such that said grooves have an non-symmetrical
appearance.
7. The end effector of claim 1, wherein said angle .theta. from a
perpendicular is about 1.degree. to 8.degree..
8. The end effector of claim 1, said end effector having an
intrusion of between about 1 mm to about 2 mm onto a back surface
of the wafer.
9. An end effector for supporting one or more semiconductor wafers
comprising:
two parallel, grooved engaging rails having corresponding linearly
aligned angled grooves adapted to engage and support a wafer at an
angle .theta. from perpendicular to said rails;
means for rigidly supporting said parallel rails in a parallel
configuration,
a non-symmetrical gripper means for association with said grooves
holding said wafer at the angle .theta. from a perpendicular with
substantially no movement of the wafer in the grooves during wet
processing; and,
one or more semiconductor wafers.
10. A method for supporting one or more semiconductor wafers during
wet processing with only two points of contact, comprising:
engaging one or more wafers with two parallel, grooved engaging
rails having corresponding linearly aligned angled grooves adapted
to engage and support a wafer at an angle .theta. from
perpendicular to said rails;
rigidly supporting said parallel rails in a parallel configuration;
and
non-symmetrically gripping said wafer holding said wafer at the
angle .theta. from perpendicular with substantially no movement of
the wafer in the grooves during wet processing.
Description
FIELD OF THE INVENTION
The present invention relates to semiconductor manufacturing.
Specifically, the present invention relates to an end effector for
supporting semiconductor wafers during wet processing.
BACKGROUND OF THE INVENTION
During wet processing of semiconductor wafers, the wafers are
exposed to various reagents. Examples of such process steps include
etching, photoresist stripping, and prediffusion cleaning. After
cleaning, the semiconductors are rinsed and dried. In order to
process wafers efficiently, they must be suspended in the various
reagents with some type of holder or carrier.
End effectors are also referred to in the art as boats, carriers,
rigs, cassettes, etc.
Semiconductor wafer carriers are used in several different types of
processing. For example, there is high temperature diffusion
processing that is carried out at temperatures from 600.degree. to
1200.degree. C. There is also wet processing which is carried out
at temperatures less than 180.degree. C. The high temperatures of
diffusion processing require that a wafer carrier designed for use
in diffusion processing must provide for substantial expansion and
warping of the wafer. In wet processing, expansion is not a
concern. Other concerns that mandate carrier design include; (1)
even and adequate contact of the wafer surfaces with the reagents,
and (2) the avoidance of trapping gases under the rails of the end
effector as the end effector is lowered into the liquid. This gas
can be released later and enter a trench on the semiconductor wafer
and block cleaning or etching of the area under the bubble.
Manual wet processing treatment typically makes use of a regular
wafer boat or wafer cassette to which a boat handle is attached for
introducing and removing the boat from the process chemistry. The
standard wafer boat for eight inch wafers has a groove larger than
the width of the wafer thickness. The wafers move back and forth
within their slots during wet processing. The standard boat
configuration for an eight inch low profile cassette cups the
entire lower half of the wafer with a six mm intrusion onto the
wafer surface. The standard configuration for a high profile
cassette contacts 3/4 inch of the wafer diameter. Typically, boats
are made of a fluoropolymer material, peek, or quartz.
In automated wet processing, the typical boat, transport rack or
cassetteless processing grips the wafer with an end effector using
a standard six mm deep v shaped groove that cups the wafers or
holds them with a minimum of 4 points of contact.
Wherever the surface of a wafer comes into contact with the wafer
carrier, there exists the possibility for imperfections in the
surface of the wafer which lowers overall yield. Most of the above
carriers and other prior wafer carriers fall into one of three
categories, namely, "four member" carriers, "three member" carriers
and "shell boats". All of these designs have a great deal of wafer
surface to carrier contact. For instance, a four member carrier
usually has four points of contact that intrude onto the wafer
surfaces. A shell boat has contact with a wafer around the entire
periphery of the wafer.
U.S. Pat. Nos. 4,493,418, 4,687,097, 4,471,716, 4,724,963,
4,949,848, and 5,111,936 are characteristic of wafer processing
cassettes known in the art for the wet processing of wafers. In
each of these patents, the wafers are held in place by cassettes
that have a great deal of contact with the wafer surfaces. In
addition to the large regions of intrusion onto the wafer surfaces,
these cassettes hold the wafers vertical with no disclosed leaning
angle.
Some of the wafer processing carriers or cassettes known in the art
of high temperature diffusion disclose cassettes that hold wafers
at a leaning angle from vertical. However, these cassettes or
carriers do not tightly hold the wafers with minimal intrusion onto
the wafer surfaces. Moreover, this design has not been employed in
carriers designed for wet processing.
U.S. Pat. No. 4,981,222 ("the '222 patent") discloses a wafer
supporting method and apparatus having at least two wafer
supporting slots for each edge-wise oriented wafer in a plurality
of coaxial edge-wise aligned wafers as depicted in FIG. 1 of the
'222 patent. The wafers are supported by either 3 or 4 round rods
as depicted in FIGS. 3, 5 and 6 of the '222 patent as well as
column 4, lines 34-35 and column 6, lines 14-18. The wafer carriers
disclosed are made of quartz and are designed for diffusion
processing at high temperatures and allow for edge to edge and
front to back translational movement during processing and
handling.
Each slot of the '222 patent has a pair of inwardly directed bevels
at the upper entrance level that may be at an angle of about
45.degree. to 60.degree. from the slot's geometrically-centered
axis. The bevels lead downwardly into a pair of parallel slot walls
that are spaced apart by about twice the thickness --2t-- of the
wafer. The rightmost wall is tangent to an arcuate-shaped bottom
wall circle having a radius of --2t--, where t is the thickness of
a wafer to be held in the slot. The longer wall of the parallel
slot walls is the wall against which the wafer will lean. Gravity
will cause the wafer to drop to the lowest point at the rounded
bottom of the slot. Accordingly, the '222 patent discloses a wafer
cassette having slots which are twice the width of the thickness of
the wafer and a rounded bottom wall thereby holding the wafer
loosely in place by the force of gravity.
U.S. Pat. No. 4,515,104 discloses a quartz boat for diffusion
processing formed with a plurality of spaced parallel rods having
slots for supporting a series of semiconductor wafers in a
generally edgewise, spaced, parallel position. The slots continue
to the ends of the rods, and the cross member supporting the rods
are spaced inwardly from the rod ends, such that a series of boats
may be arranged with the rods in end-to-end relation and the wafer
space between adjacent boats is the same as the wafer space in the
middle of a boat. Little detail is disclosed regarding the shape of
the slots or the freedom of movement the wafers have when seated in
the slots. The drawings disclose a boat with 4 points of contact
intruding onto the wafer surfaces.
U.S. Pat. No. 4,053,294 discloses a semiconductor boat or carrier
with three slotted points of contact intruding onto the wafer
surfaces. The grooves are beveled and symmetrical about the
centerline of the groove.
A problem associated with most of the above-described designs is
that die yield at the edges of the wafers is sacrificed because the
active surface area of each wafer is diminished by the intrusion of
the end effector. The further the end effector intrudes into the
wafer surface, the larger the area on the outer surface of the
wafer that is rendered useless. Particle generation can also be a
problem where the wafers are free to move around within the
grooves. The wafers rattle about within the grooves, colliding with
the inner surfaces of the groove thereby chipping away at the wafer
or the rack which produces particulate contamination.
Another problem with boats such as those above-described is that
they are difficult to clean. The greater the number of grooves, the
more difficult the carrier is to clean. Also, cassettes with deep
grooves are more difficult to clean. Horizontal surfaces and points
where rods connect result in places that trap liquids and
particles.
Another problem with many of the above-mentioned wafer carriers is
that they are made of materials which have undesirable properties
for wet processing. For instance, teflon absorbs process chemicals
which are later outgassed, forming a haze or unwanted etching on
the surfaces of the adjacent wafers as well as damage to other
equipment downstream of the wet station. Teflon also creates
particulate contamination thereby decreasing wafer yield. Teflon is
soft and is easily scored by silicon wafers and this can create
particle contamination as well as trap the edge of the wafer within
the teflon. This can lead to wafer breakage when the wafer is moved
perpendicular to the direction it is held or trapped (which
frequently occurs in a spin dryer). Carriers made from PEEK (poly
ethyl ether ketone) are not suitable for processes completed at or
above 100.degree. C. such as piranha or phosphoric cleaning. Quartz
carriers are too fragile and the grooves deteriorate. This often
leads to adherence of the wafer to the quartz. Removal of a disc
that has adhered to the quartz carrier usually results in breakage
of the wafer. Also, quartz carriers are incompatible with
hydrofluoric acid.
Accordingly, it is an object of this invention to provide for an
end effector that holds a plurality of wafers tightly with only two
points of contact that minimally intrude onto the wafer
surfaces.
It is further an object of the present invention to design a wafer
end effector that is easily cleaned.
It is further an object of the present invention to design a wafer
end effector that holds a plurality of wafers at a slight angle
from vertical.
It is yet another object of the present invention to provide a
lightweight, sturdy end effector made of a material which minimizes
particle generation and is chemically inert.
These and other objects of the present invention will become
apparent upon a review of the following specification and the
claims appended thereto.
SUMMARY OF THE INVENTION
The foregoing objectives are achieved by an end effector for
supporting one or more semiconductor wafers during wet processing
comprising two parallel, grooved engaging rails having
corresponding linearly aligned angled grooves adapted to engage and
support a wafer at an angle from perpendicular to the rails, means
for rigidly supporting the parallel rails in a parallel
configuration, and a non-symmetrical gripper means for association
with the grooves holding the wafer at the angle from perpendicular
with substantially no movement during wet processing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts a head-on view of an end effector according to the
present invention.
FIG. 2 is a side view of the end effector of FIG. 1.
FIG. 3 depicts the angled grooves with the non-symmetrical gripping
means of the present invention at the bottom of the grooves.
FIG. 4 is a magnified view of a single angled groove of FIG. 3.
FIG. 5 is a view of the parallel slotted engaging rails on an x, y,
z axis.
FIG. 6 depicts one embodiment of the angled grooves of the present
invention.
FIG. 7 depicts yet another embodiment of the angled grooves of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The apparatus of the present invention is an end effector for
supporting one or more semiconductor wafers during wet processing
comprising two parallel, grooved engaging rails having
corresponding linearly aligned angled grooves adapted to engage and
support a wafer at an angle from perpendicular to the rails, means
for rigidly supporting the parallel rails in a parallel
configuration, and a non-symmetrical gripper means for association
with the grooves holding the wafer at the angle from perpendicular
with substantially no movement during wet processing.
The end effector of the present invention is made from any
substance chemically inert and resistant to cracking, chipping,
flaking or other particle generation. This includes quartz, peek,
teflon, other fluoropolymers and, preferably, a woven carbon
composite which has either a CVD or sputtered coating to eliminate
particle generation and ensure chemical inertness. Without such a
coating, materials such as teflon may blister over time from
continued exposure to cleaning using megasonics. Blistering then
leads to shedding of particulates. The coating will vary depending
on the liquid in use and the temperature range. The coatings
include silicon nitride, carbon nitride, polysilicon, silicon
carbide and a carbon coating. These coatings do not absorb
chemicals in contrast to materials such as teflon. Performance is
optimized for different processing chemicals by selecting the
proper coating. Accordingly, metals leaching from the boats into
the chemical baths and partial shedding or breakdown of the end
effectors can be minimized by the use of the proper coating.
The two point wafer contact end effector with 2 mm or less
intrusion of the present invention increases the active wafer
surface or number of devices which can be manufactured on the wafer
surface. Other advantages include: (1) the elimination of shielding
of the wafers in in-situ gas generated liquid processing, such as
that disclosed in copending application Ser. No. 08/092,523, hereby
incorporated by reference, (2) increased cleaning efficiency, for
example, with megasonic cleaning action because there is less
interference from the end effector with the cleaning process, (3)
the amount of liquid dragged out of solution and carried over to
the next process tank is minimized, and (4) drying efficiency is
maximized because there are no horizontal surfaces to trap liquids
or particles and particulates are minimized.
The basic structure of the end effector according to the present
invention includes a set of two grooved parallel rails rigidly
supported by a means for rigidly supporting the parallel slotted
rails such that the parallel formation of the rails is
maintained.
By parallel formation it is meant that on an x, y, z axis where the
rails lie horizontal to the x, z plane, the rails are parallel when
viewed from the y-axis. This is depicted in FIG. 5. In FIG. 5, it
can be seen that rails (99) and (100) in the x, z plane are
parallel when viewed from the y-axis.
The parallel grooved rails may have any of a variety of shapes when
viewed from an end. For instance, the rail may be in the form of a
dowel having a circular end. The rails may also be hollow. The rail
may have a square or rectangular shape when viewed from an end.
Thus, the particular shape of the rail when viewed from an end is
not critical to the invention so long as the combination of rails
is parallel and evenly spaced. However, a diamond shaped, or
circular rail is preferred to eliminate liquids adhering to the end
effector. The diamond shaped rail has points of the diamond being
located at 0, 90, 180 and 270 degrees from the 12 o'clock position
when viewed from an end to facilitate liquid sheeting of the rails.
The square or horizontal surfaces when viewed from the top can be
detrimental to liquid processing because they tend to trap
liquids.
The grooved rails are supported by a means for rigidly supporting
the parallel rails in a parallel configuration. This can be
accomplished by any number of structures well known in the art. In
one embodiment depicted in FIGS. 1 and 2, a pair of endplates (1)
are rigidly fastened to parallel rails (3) and (5). This could also
be accomplished by other structures such as end blocks with
receiving slots for the parallel grooved rails or support rails
running between the parallel grooved rails.
The rails are spaced apart at a distance such that the each rail
engages and supports the edge of the bottom half of a wafer at
point along the circumference about 45.degree. to each side of
bottom center. It should be appreciated that the particular angle
of engagement from bottom center about the circumference of the
wafer is not critical to the present invention. However, the wafer
is preferably only supported by two points below the horizontal
centerline of the wafer. When looking at the surface of the 200 mm
wafer, the first contact point would be any point less than the 9
o'clock position, but greater than the 6 o'clock position.
Likewise, the second point would be any point less than the 6
o'clock position, but greater than the 3 o'clock position. In
practice the two points are chosen to be equidistant about the
lower arc of the circle, such as 5 and 7 o'clock positions or 4 and
8 o'clock positions, but they are not required to be equidistant.
For instance, points of contact at 4 o'clock and 7 o'clock would
work.
Each of the parallel grooved engaging and supporting rails has a
series of angled grooves for receiving wafers at an angle .theta.
from perpendicular to the rails. Accordingly, each groove on one
engaging rail has a corresponding aligned angled groove on the
other engaging rail such that a wafer supported by the engaging
rails sits in a linearly corresponding angled groove in each
engaging rail. Angle .theta. can be between 1.degree.-8.degree.
from perpendicular and is preferably between 1.degree. and
5.degree. from perpendicular.
The non-symmetrical gripper means according to the present
invention is comprised of any number of tapered cuts forming the
above-mentioned grooves. The gripper means should be unsymmetrical
about a vertical line drawn from the deepest point in the groove up
a point level with the top of the groove.
FIG. 3 depicts a series of angled grooves as they appear on the
surface of a single grooved rail of one embodiment of the present
invention. FIG. 4 depicts a magnified view of a single groove from
FIG. 3. As seen in FIG. 4, each groove has a flaired portion (50)
on each side of the top of the groove. Each groove also has an
non-symmetrical gripper means which is comprised of right taper
(53) and left taper (54). Tapers (53) and (54) are cut at such an
angle that they provide an non-symmetrical seat for receiving a
wafer. The tapers may be comprised of one or more distinct surfaces
that intersect to form the bottom of the groove. The specific cut
of the tapers or number of taper cuts is not critical to the
present invention so long as the non-symmetrical gripper means is
capable of holding the wafer at a slight angle from vertical with
substantially no movement during processing. In this regard, an
additional taper (55) is depicted in FIG. 4.
FIG. 6 depicts one embodiment of the angled grooves of the present
invention. Depth (79) is the total depth of the groove which is
3.175 mm. Flairs (80) and (81) are angled about 30.degree. to
either side of vertical, meeting first taper surfaces (82) and (83)
which in turn meet second taper surfaces (84) and (85). Taper
surfaces (84) and (85) are cut at different angles such that each
taper surface is a different length. The non-symmetrical nature of
the gripper means enables the groove to hold the wafer with
substantially no movement during processing at a slight angle from
vertical.
FIG. 7 depicts yet another embodiement of the present invention
with an alternative groove design.
Both FIGS. 6 and 7 depict the holding of wafer 110. As seen in the
figures, the wafers only have three contacts with the groove, of
which only one contact touches the surface of the wafer. The other
two contacts are with the outer edges of the wafer. Accordingly,
die yield is maximized. Preferably, only the back surface of the
wafer is in contact with the groove as depicted in FIG. 4.
By substantially no movement during processing it is meant that the
wafers do not slide or rattle around within the grooves during
processing. The wafers are held tight and firm such that there is
little or no room for expansion of the wafer. The wafer is not free
to move within the slots.
It is also important that the grooves of the present invention
provide minimal intrusion onto the surface of the wafer. As set
forth above, for example, this means a maximum intrusion of 2 mm
for a 20 cm wafer. Preferably, the intrusion is close to 1 mm as
opposed to prior art end effectors which have 6 mm intrusion. The
intrusion onto the surface of the wafer is the distance onto the
front or back surface of the wafer which has contact with the
groove or gripper means of the present invention. A minimal
intrusion enhances product yield.
In one embodiment of the present invention, one or more additional
supporting non-engaging parallel rails are included. The additional
non-engaging rails parallel to the two engaging rails, sit at
points corresponding to the circumference of the bottom half of the
wafer between the two engaging parallel rails as shown in FIG. 1 at
(8). The additional rail or rails do not engage the surfaces of the
wafer as do the engaging parallel rails. They merely provide
structural rigidity to the end effector. They are not in contact
with the wafer. They provide for rigidity in the "Z" direction when
attached to the endplates.
While this invention has been illustrated and described in
accordance with a preferred embodiment, it is recognized that
variations and changes may be made therein without departing from
the invention as set forth in the claims.
* * * * *